In electronic devices such as a smartphone, a tablet terminal, a notebook computer, a portable audio device, a digital camera, a game machine, and a car navigation device, it recently is becoming more standard to have an input device to operate the electronic devices with a touch or contact of a finger. As such an input device, a resistive touch panel (touch sensor) or the like is known.
FIGS. 1A and 1B are views illustrating a structure of a resistive touch panel. The resistive touch panel (hereinafter, simply referred to as a “touch panel”) 900 includes a first resistive film 902 and a second resistive film 904. The first resistive film 902 and the second resistive film 904 are installed to be spaced apart from each other in a Z direction. A first electrode 906 and a second electrode 908 are formed in the first resistive film 902 along two sides extending in an X direction. A third electrode 910 and a fourth electrode 912 are formed in the second resistive film 904 along two sides extending in a Y direction. Lines (or terminals) XP, XN, YP, and YN connected to the four electrodes are drawn out from one common side 914.
A touch is detected in a state where a predetermined voltage VP is applied to the line XP and a voltage VN is applied to the line YN. In this state, when the user's finger makes a contact with the touch panel 900, an electrical state, i.e., a voltage or a current, generated in the lines XN and YP is changed depending on contacted coordinates. Thus, the coordinates may be calculated by measuring the electrical state of the lines XN and YP.
In FIG. 1B, a cross-section of a joint part of a resistive film 920 and an electrode 922 is illustrated. Since the electrode 922 has a certain height h, a dead space (invalid region) 924 where coordinates cannot be detected exists near the electrode 922. Thus, a width (length) of the panel becomes longer by the invalid region than a width (length) of a region available for a coordinate detection. While a size of the invalid region largely relies on a material or a manufacturer of a resistive film or an electrode, the size of the invalid region is generally about 0.4 mm to 10 mm. When an area of the touch panel 900 is sufficiently large, the invalid region is not problematic. However, when invalid regions of 1 cm are required at both ends, for example, in a 3 cm-panel, a valid region becomes merely 1 cm.